It is generally known to supply commercial aircraft with conditioned air for heating and cooling when the aircraft is stationary at a gate. In this document, the term gate is meant to refer to any place that an aircraft receives or discharges passengers or cargo. This may be by way of a telescoping corridor (also referred to as a walkway, bridge way, jet bridge), stairs, or any other facility. Typically, conditioned air is supplied to the aircraft from a pre-conditioned air (PCA) unit associated with the gate that is a part of the airport terminal. The PCA unit may produce heated air or cooled air depending on the needs of the aircraft it is servicing. The PCA outputs its air into a duct that may be rigid or flexible, and then the air is delivered from the gate to the aircraft with a flexible and usually insulated air hose.
Devices for deploying and retracting a hose are known, for example in U.S. Pat. Nos. 6,821,201, 6,776,705, and 6,834,668 to Bombardi et al. In a retractable hose device such as described by Bombardi, the power required by the dispensing and retracting device to reliably do its job varies with the length of the hose installed in the device, temperature, and a variety of factors. For example, a long hose, due to weight and drag, requires a different level of energy to retract it than does a short hose. Further a hose that becomes wrapped around an obstacle may stop moving entirely. An improved device is described in the above-referenced U.S. patent application Ser. No. 12/025,022 filed Feb. 2, 2008 by Wright et. al, and hereby incorporated by reference in its entirety. In at least one embodiment, the hose management system in the Ser. No. 12/025,022 application has torque sensing circuitry that is adjustable according to the hose installed. Further, this torque sensing circuitry is employed to stop the retracting motor should it sense a high level of torque, indicating that the hose is snagged on an object, for example a baggage cart. However this method of detecting a snag to stop the motor sometimes fails to work. This failure may occur, for example, if the torque sensing circuitry is set to respond at a value greater than the force generated by the tread slipping over the surface of the hose. In such cases, the hose remains still while the treads keep moving, abrading and damaging the stationary hose. Therefore there is a need for an improved device to stop the tread from trying to move the hose, when the hose is unable to move.